Lithium nickel ferrites



June 12, 1962 F. E. VINAL ETAL 3,038,360

' LITHIUM NICKEL FERRITES Filed Dec. 20, 1956 4 Sheets-Sheet l A AAVAYAYAYMYAYAYAYAYAVAYAVA #YLYAYAVAVYAYAYYAYAYAYAVA 'o.5 2 5 4)1 AAAAAAAAAAA AVAVYAVAYA AVAYAYAVAYAVAYAYAYAYAYAAVAVAYAVAVAKYMVAVAYAYAYAVAVAVAVAVA vvvvvvvnvvvvvvvvvv N'Q NiFe204 2 3)CURIEY TEMPERATURES IN c 2 4) AND SQUARENESS RATIO CONTOURS INVENTORS.

FRANCIS E. VINAL y DANIEL L. BROWN AGENT June 12, 1962 -F. E. VINALIETAL 3 I LITHIUM NICKEL FERRITES Filed Dec. 20, 1956 4 Sheets-Sheet 2 55 3 I (Zn Fe O AYAAAA AYAYAVAYAYA AYAYAYAYAVAYA I AVAYAYAYAYAYAYAYYYYYYV /V\/\/\/\/\/\/\/\/\/\ SQUARENESS RATIO CONTOURS AND CURIETEMPERATURES IN C INVENTORJI.

FRANCIS E. VINAL BY DANIEL Lv BROWN AGENT June 12, 1962 F. E. VINAL ETAL3,038,860

LITHIUM NICKEL FERRITES Filed Dec. 20, 1956 4 Sheets-Sheet 3 SQUARENESSR ATIO, R S

O V 25 5O 75 100 MOLE PERCENT NICKEL FERRITE IN LITHIUM'NICKEL FERRITEINVENTORS.

, FRANCIS E. VINAL BY DANIEL L. BROWN AGENT June 12, 1962 F. EQVINALETAL 3,038,360

LITHIUM NICKEL FERRITES Filed Dec. 20, 1956 4 Sheets-Sheet 4 OUTPUT(m.v.)

CALCINATION TEMPERATURE (C) INVENTORS.

FRANCIS E VINAL DANIEL L. BROWN AGENT Unite tats 3,038,360 LITHIUMNECKEL FERRITES Francis E. Vinal, Weston, and Daniel L. Brown, Boston,Mass, assignors, by mesne assignments, to the United States of AmericaFiled Dec. 20, 1956, Ser. No. 629,666 6 Claims. (Cl. 252-625) Thisinvention relates to a process for manufacturing ferromagnetic ceramicproducts and to the products so produced. More particularly, thisinvention relates to improved materials of the class known asferrites,.composed of spinel compounds formed from the oxide groupincluding lithium oxide, nickel oxide, iron oxide, zinc oxide andcadmium oxide. Ferromagnetic ceramic bodies have wide technicalapplications, two examples for bodies having hysteresis loops ofsubstantially rectangular shape being switching arrays andmulti-coordinate memory devices for use in the computing field. Ferritecores with usable properties are now available, the cores normally beingformed from compositions containing compounds of manganese, magnesiumand iron.

Magnesium-manganese ferrite cores posses a Curie temperature in thevicinity of 250 C., such that elevated ambient operating temperaturesmust be avoided, yet the.

cores normally have high coercive forces resulting in the requirement ofcomparatively high driving currents to alter their magnetic state. Suchconflicting requirements have been met in part by air cooling and closetemperature control. The materials of the present invention have beenfound to possess improved magnetic properties, Le. a higher Curietemperature in the order of 600 C. and with substantially rectangularhysteresis loops. Thus, products made from the materials of thisinvention can be used at higher ambient temperatures or, more important,with higher energy dissipation than hereto-fore. The coercive force isapproximately the same as that of materials in present use, beingsomewhat higher or somewhat lower depending upon which of thecompositions disclosed is employed.

In some applications ferromagnetic ceramic bodies which have highsaturation flux densities, but not necessarily rectangular hysteresisloops, are desirable. Magn esium-managanese ferrites have been modifiedby additional elements to increase saturation flux densities. Thesemodifications normally produce a lowering of the Curie temperatures tovalues too low for satisfactory use in many applications. Materials ofthe present invention provide high saturation flux densities with Curietemperatures higher than unmodified magnesium-manganese ferrites.

In general, it is known that the ferrites, which are cubic crystallinematerials containing Fe O and at least one other oxide, may beconsidered to be polycrystalline preparations of mixed crystals of theconstituent compounds. The present invention, therefore, contemplatescombining the constituents in proportions calculated to make chemicallystoichiometric mixtures and controlling the conditions of the process tominimize loss of any metal oxide during the sintering operation.Although there have been references to lithium-nickel ferrites in theliterature, notably 3,938,86 Patented June 12, 1962 Wijn et al. inPhilips Technical Review, August 1954, pages 49 to 58, the processes bywhich useful products are obtained are not taught therein.

An obiect of this invention is to provide lithium-nickel ferritecompositions and processing methods suitable for the production offerromagnetic ceramic products with hysteresis loops of substantiallysquare or rectangular s ape.

Another object of this invention is to provide lithiumnickel ferritecompositions and processing methods suitable for the production of coreswith short switching times.

Another object of this invention is to provide lithiumnickel ferritecompositions and processing methods suitable for the production ofsquare loop products with high Curie temperatures.

A further object of this invention is to provide high saturation fluxdensity lithium-nickel ferrites with high Curie temperatures.

These and other objects are obtained by utilizing a composition composedof compounds from the group including iron oxide, lithium oxide, nickeloxide, zinc oxide, and cadmium oxide and processing the composition asspecified in this invention.

FIGURE 1 is a chart of composition ranges.

FIGURE 2 is a chart of composition ranges.

FIGURE 3 is a chart of composition ranges.

FIGURE 4 is a graph of squareness ratio plotted against percent nickelferrite.

FIGURE 5 is a plot of a hysteresis loop.

FIGURE 6 is a graph of output voltages for a core being tested for usein coincident current. memory application.

FIGURE 7 is a graph of calcination temperature plotted agalnstsquareness ratio.

The process of this invention is in its general aspects very similar tothat currently employed for the production of ferromagnetic ceramicsfrom compositions composed of the oxides of iron, magnesium andmanganese. The first step is the intimate mixing of the properproportions of the oxides involved, each in a fine state of subdivision.Instead of startingwith the oxides themselves it is possible to startwith a mixture materials in other than the oxide form, provided thestarting materials will be changed to the specified oxideduringprocessing. For example, it has been found that the use of thecarbonates is convenient. The next step, if carbonates have been used,is calcining at approximately 600 C. to 850 C. for two to twenty hours.Calcining for a longer period, while unnecessary, does not appear to beharmful. The calcining step drives off the CO from the carbonates andmay result in some reaction. The fact that Li CO melts at approximately635 C. is of no concern because this compound is present in such arelatively small amount and its de composition is effected during thereaction that takes place during calcining. Experimental results haveshown that the magnetic properties of the final product can be improvedby controlling the calcination temperature.

In general, for each compositional mixture there can be found acombination of calcining temperature and time which results in thegreatest squareness.

Most of the data in this specification is taken from range surveys.Therefore, characteristics of specific compositions are subject to someimprovement by adjusting processing parameters for the specificcomposition.

FIGURE 7 contains plots of the squareness ratio versus calcinationtemperature for mixtures lying at the NiO point on line 1 of FIGURE 1.It will be seen that optimum squareness results over a to range ofcalcination temperature. In general, as the percent NiO.Fe O increases,the optimum calcining temperature increases. The temperature is,however, kept below that required for sintering and full reaction.Calcining as described results in material soft enough that no grindingis required at this point, although a grinding operation may be employedif desired. The third step is the addition of a binder. The particularbinder used is not criti- URE 1. This figure represents all possiblecombinations within the ternary system:

Fe O I I TABLE I Magnetlc Properties of Lrthmm-Nzckel Ferrztes Molpercent as mixed R, Bm H H0 B,1 H Slnterlng temp. 0. L110 NlO F9203 16.7 0 83.3 .50 1,080 2. 5 1. 5 2,960 2. 3 1, 200 15.8 2.5 81.6 .70 1, 4802.0 1.2 2,600 1.6 1,200 15.0 5. 0 80.0 .81 1, 600 2. 3 1. 5 3, 000 2. 01,250 13. 3 10.0 76. 7 .81 1, 700 2. 2 1. 2 3, 200 1. 5 1,275 11.7 15. 073. 3 .72 1, 340 1.8 1.1 2, 750 1. 5 1,275 10. 0 20. 0 70. 0 72 1, 0402. 0 1. 3 2, 610 1. 7 1,275 a. 3 25. 0 66. 7 .41 770 2. 3 1. 4 2, 780 2.0 1, 275 6. 7 30. 0 63. 3 .48 490 2. l 1.3 2, 300 2.0 l, 275 3. 3 40. 056. 7 .57 600 1. 9 1.3 2, 300 1.8 1, 275 0 50.0 50. 0 .40 1, 060 6. 9 2.4 2, 100 5. 3 1, 250

H... is in oersteds.

cal. The trade preparation Flexalyn, for example, has proved quitesatisfactory. The fourth step is pressing the resulting mixture into thedesired form. The pressure of forming should be suflicient to form aclosely coherent body. The pressures used should be simply thosenecessary to obtain this result. 30,000 pounds per square inch hasproved to be quite satisfactory. The forms may be produced by extrusionprocesses if desired. Usually extrusion processes are less costly butmake it more difficult to hold close tolerances. The fifth step is thesintering of the resulting forms. Satisfactory results have beenobtained with sintering temperatures from 1150 C. to 1325 C. andsintering times from one to ten hours. Excessive coercivity results ifsintering temperatures below that recommended are employed. In general,the highest sintering temperature permissible for satisfactory productsincreases with a decrease in the percentage of lithium in thecomposition. A slab containing compounds of lithium is used to supportthe forms being fired. It is desirable that the percentage of lithium inthe slabs be at least equal to that in the forms. The use of slabs ofthe same composition as the ferrites being fired is a convenientexpedient. The use of these slabs containing lithium appears to minimizethe loss of lithium from the forms during the firing operation. It is inthis step that this invention differs importantly from processescurrently in use.

The forms are not quenched after firing, but rather held in the furnaceat 1000 C. to 1125 C. for six to ten hours. This anneal appears toimprove magnetic properties, and inadequate annealing may be correctedby a refiring at annealing temperatures. This refiring need not be in aneutral atmosphere but may be in the normal atmosphere of the furnace.In fact, refiring in a moving neutral atmospherethe customary techniquefor refiring in a protective atmosphere-has proved harmful, probablybecause of increased loss of lithium.

The compositions involved in this embodiment of the invention may bestbe understood by reference to FIG- Referring to FIGURE 5, the squarenessratio R is defined as The denominator and enumer ator of the latterrepresent respectively the magnetization for a field |I-I and that for afield /2H It will be clear that R is also a function of the maximumfield H determining the size of the loop. When R is measured as afunction of H,,,, a value of 11 will be found for which R is at amaximum. In practice, an effort is normally made to use cores underconditions such that R is at or near the maximum value. If thehysteresis loop were perfectly rectangular, the squareness ratio would,of course, be 1. Practically achieved squareness ratios are always lessthan 1 with .80 being the figure most often used as the minimumacceptable for applications requiring substantially square orrectangular hysteresis loops. It will be noted that'FIGURE 4 shows thatsquareness ratios as high as .83 have been obtained. The maximumsquareness ratio shown in the aforementioned Wijn paper is .78. If .80is taken as the minimum acceptable squareness ratio, satisfactoryresults with the particular processing conditions used to obtain thedata for FIGURE 4 were obtained over that portion of the line includedbetween 7 to 30 percent NiO.Fe O If the cores are to be used inapplications with less stringent squareness requirements so thatsquareness ratios of 0.6 and above may be tolerated, satisfactoryresults were obtained over that portion of the line included between 3to 45 percent NiO.Fe O

The hysteresis loop obtained with a sample from the 9% nickel ferritepoint on line 1 of FIGURE 1 is shown in FIGURE 5. The squareness ratioof this particular sample is .81. The dynamic result obtained in a testof the suitability of this sample for use in a magnetic core memory isillustrated in FIGURE 6. Line 10 in FIGURE 6 is the maximum allowableoutput from a half selected core; line 11 is the minimum allowableoutput from a fully selected core. For this particular memory, theselimits are 30 and 80 millivolts respectively. The driving current forthe test was 900 milliampe'res with a 2 to 1 selection ratio. Thesmallest divisions along the horizontal or time axis are .2 of amicrosecond. It will be seen that this core switches in approximately 1microsecond. It will be noted that the output as a selected core issubstantially greater than the accepted minimum for this particularmemory and that the output as an unselected core is substantially lessthan the accepted maximum.

Table II contains a tabulation of squareness ratios for varyingcompositional mixtures including mixtures which are not s'toichiometricand, therefore, do not lie on line 1 of FIGURE 1. These compositions andsome of the Curie temperatures are plotted in FIGURE 2.

TABLE II Magnetic Properties of Lithium-Nickel Ferrites (Non-Stoichiometric) included as one of the components in the lithiumnickel ferrite, the coercive force is substantially reduced. LithiurnZinc fenrites are not rectangular hysteresis loop materials. However, byincludingzinc in the lithium nickel ferrite materials that possessrectangular hysteresis loops, relatively low coercivities andsubstantially higher flux densities can be obtained. Coercivity isreduced with increasing proportions of Zinc ferrite in the composition,

M01 percent as mixed R Bm H... H.; B H Sintering temp. 0.

L110 N10 F6203 17. 7 O 82.3 .63 1, 140 2. 4 1. 5 2,660 2. 1 1, 175 17.2 1. 3 81. 5 63 1, 300 2. 5 1. 6 2, 900 2. 1 1, 175 1G. 8 2. 5 80. 7 781, 320 2. 4 1. 5 2, 800 2.0 1,175 16. 8 3. 8 79.8 78 1, 300 2. 4 1. 6 2,720 2.] 1,175 15. 9 5. 1 79. 81 1, 400 2. 4 1. 2, 710 2. 0 1, 175 15.56. 4 78.1 77 1, 210 2. 4 1. 5 2, 790 2.0 1,175 15.0 7. 7 77. 3 .76 1,230 2. 6 1. 7 2, 750 2. 0 1, 175 14. 1 10. 2 75. 7 75 1, 030 4. 2 2. 62, 680 3. 6 1,175 13. 3 12. 7 74. 0 69 830 3. 8 2. 4 2, 580 4. 2 1, 17512. 4 15. 3 72. 3 .48 750 2. 7 1.6 2, 660 2.6 1, 175 10. 6 20. 4 69. 0.27 840 4. 0 2. 3 2, 490 3. 4 1, 175 16. 3 3.8 79. 8 .63 1,000 2.0 1. 22, 980 1. 9 1, 250 15.9 5. 1 79. 0 78 1,070 2.0 1. 3 2, 310 1. 7 1, 25015.5 6. 4 78. 1 74 1, 450 2.0 1. 3 3,080 1. 8 1, 250 15.0 7. 7 77.3 701, 340 2. 2 1. 4 2, 800 1. 9 1,250 14. 1 10.2 75. 7 68 1, 290 2. 7 1. 72, 800 2. 2 1, 250 16. 3 3.8 79.8 .62 1, 300 2. O 1. 2 2, 780 1. 8 1,300 15. 9 5.1 79. 0 .68 1, 260 1. 8 1. 2 2, 690 1. 6 1, 300 15.5 6. 478. 1 .69 1, 360 1.8 1. 2 2,750 1. 7 1, 300 15.0 7. 7 77.3 63 1, 230 1.9 1. 2 2, 830 1. 7 1, 300

and H... is in oersteds.

The ternary system of FIGURE 2 is F203L1FO2IN1F204 This system, which isactually a portion of that shown in FIGURE 1, has been chosen to expandthe scale at which these results are plotted. It will be noted thatlower squareness ratios and increased coercivity results fromcompositional variations in directions normal to the stoichiometricline. It is thought that excess Fe O gives precipitated iron oxide and/or solid solution magnetite in the resulting material. It is thoughtthat excess Li O gives a rock salt structure (LiFeO instead of a spinalstructure Li Fe O The degradation of characteristics occurs more rapidlyfor excesses of Fe O than for excesses of Li O. The aforementioned useof slabs containing lithium to minimize the loss of lithium during thefiring operations is important in that it minimizes unwantedcompositional variations from the stoichiometric line with the resultingdegradation of magnetic properties.

The values tabulated in Table II are from a range survey, and themagnetic properties of any specific composition may be improved byadjusting processing parameters. The previously noted variation ofsquareness ratio with calcination temperatures shown in FIGURE 7 is anexample of the improvement possible by adjustment of but to maintainsquareness, the percentage of nickel ferrite must also be increased.Increasing the percentage of nickel ferrite tends to increasecoercivity. The best compromises with respect to high squareness and lowcoercivity are normally obtained from compositions with approximatelyone to one mol percent ratios of zinc and nickel ferrites. The additionof Zinc ferrite to the lithium nickel ferrite lowers the Curietemperature. However, the Curie temperature of the lithium nickelferrite is relatively high so that even after an appreciable amount ofZinc ferrite has been added, about 35 mol percent, the Curie temperatureof the resulting composition is still around 400 C., considerably higherthan that for magnesium manganese ferrites in current use. Theprocessingconsiderations are the same whether or not Zinc ferrite is a component,with the exception that longer annealing times, up to twenty-four hours,are desirable.

Compositions within the ternary system are shown in FIGURE 3. Table IIIcontains a tabulation of properties for several of these compositions.

TABLE III Magnetzc Properties of Lzzhzum-Nlckel-Zmc F errztes Ferrites,mole percent as mixed Sintering s in Hm H B 5 H55 Temp. "C

Li Ni Zn 90 5 5 .45 1, 580 1. 63 0. 99 3,690 1. 63 1,250 85 16 5 .60 1,490 1. 66 1. 02 3, 420 1. 66 1,250 80 16 .69 1, 996 1. 66 1. 65 3,650 1. 66 1, 256 75 16 .40 1, 366 1. 74 1. 02 3, 396 1. 86 1, 256 75 5.73 1, 660 2. 65 1. 23 3, 136 2. 69 1,250 70 15 15 .59 930 1. 47 6. 933, 696 1. 47 1,250 65 36 5 .65 1, 450 2. 31 1. 49 3, 266 2. 39 1, 200 6520 15 67 1,176 1. 31 6. s4 3, 420 1. 35 1, 256 66 23 17 72 1, 340 1. 210. 7s 3, 576 1. 23 1,206 60 20 20 63 1, 340 1. 15 0. 73 3, 470 1. 151,260 60 15 39 0 1. 18 6. 70 3,230 1. 14 1, 260 55 40 5 .44 1, 360 2.21 1. 33 3, 166 2, 21 1,260 55 3 15 .76 1, 0 1. 34 6. 86 3, 600 1. 32 1,206 55 25. 7 19. 3 75 1, 540 1. 22 6. 73 3, 956 1. 20 1, 250 55 20 25 501, 396 1. 22 0. 73 3, 390 1. 17 1, 250 56 28. 5 21. 5 71 1,610 1. 0.823, 650 1. 26 1,225 50 25 25 67 1, 890 1. 20 0. 77 3, 560 1. 10 1,225 5620 30 43 1, 250 1. 19 0. 72 3, 330 1. 10 1,250 43 32 20 46 1, 440 1. 620. 60 3, 650 0.89 1, 175 45 20 35 1, 160 1. 69 0. 63 3, 610 0. 99 1,25045 31. 5 23. 5 65 1, 440 1. 20 0. 74 3, 916 1. 20 1, 225 45 35 2 64 1,416 1. 4o 6. 88 3, 390 1. 1,225 30 25 69 1, 896 1. 20 0. 77 3, 560 1.161,225 42 2s 30 64 1, 676 1. 14 0. 73 3,850 1. 14 1, 175 40 45 15 65 1,550 1. 10 0. 65 3, 630 6. 97 1,225 40 46 20 .44 1, 170 1. 40 0. 90 3,396 1. 30 1, 225 40 30 36 68 1, 520 1. 16 0. 76 3,790 1. 10 1,225 40 2535 60 1, 640 1. 19 0. 73 3, 390 1. 09 1,225 46 20 46 .31 916 0. 91 0. 533, 470 6. 84 1,200 35 37. 5 27. 5 .46 1, 160 1. 15 0. 69 4, 020 1. 091,225 35 35 30 88 ,350 1. 02 0. 59 3, 896 0. 90 1,225 35 30 25 53 1,230 1. 69 o. 66 3, 460 6. 98 1,225 35 25 40 .35 1, 050 0. 90 o. 53 3,346 0. 83 1, 200 36 46 30 .48 1, 410 1. 28 0. 76 3, 440 1. 09 1,225 3037 33 .41 1, 050 1. 07 0. 62 3, 700 0. 65 1, 256 30 35 35 .64 1, 550 1.09 0. 65 3, 630 6. 97 1,225 30 36 40 .38 1, 010 0. 91 6. 53 3, 080 0. 861,260 20 30 36 1, 690 0. 94 6. 56 4,250 0. 94 1,250 20 42 3s 32 970 0.95 0. 66 3, 580 0. 68 1, 260 100 0 o .59 1,260 2.9 1. 9 2, 766 2.8 1,26090 0 1O 44 l, 080 1. 5 9 3, 130 1. 4 1, 200 80 0 20 .24 180 1. 5 .9 3,810 1. 4 1,260 70 6 30 13 1, 570 1. 4 .8 4, 216 1. 2 1,200 0 40 16 1,446 1. 1 6 4, 646 .9 1, 206 50 0 50 09 1,140 .9 .4 3, 920 .7 1, 206

H5, is in oersteds.

The values tabulated above are from a range survey, and the magneticproperties of any specific composition may be improved by adjustingprocessing parameters.

If 0.80 is taken as the minimum acceptable squareness ratio,satisfactory results can be obtained with compositions lyingapproximately within area A in FIGURE 3. If the cores are to be used inapplications with less stringent requirements so that squareness ratiosof 0. 6 and above may be tolerated, satisfactory results can be obtainedwith compositions lying approximately within area C on FIGURE 3. Thechange in squareness ratio with compositional variations is not as rapidin the system of FIGURE 3 as in the system of FIGURE 2. Therefore, areaB has been outlined on FIGURE 3 to show the approximate area in whichsquareness ratios of 0.7 and above can be obtained. It may be noted thatthe region of highest squareness in the lithium nickel zinc ferrite whenextrapolated to the stoichiometric line between lithium ferrite andnickel ferrite shown on FIGURE 1 coincides very well with the optimumregion indicated on FIGURE 2 for lithium nickel ferrites which do notinclude zinc fenrite.

' For applications which do not require rectangular hysteresis loops,the compositions lying within area D on FIGURE 3 provide high saturationflux densities with relatively high Curie temperatures. The area of highpermeability extends, theoretically, to some point near 100% ZnFe OHowever, increases in the zinc ferrite content progressively lower theferromagnetic Cun'e temperature. Therefore, unless the ambienttemperature is lowered as the Curie temperature is decreased, thepermeability goes through a maximum as the amount of ZnFe O isincreased. By virtue of the high Curie temperature of the lithium-nickelferrites, around mol percent ZnFe O can be tolerated if the products areto be used at normal ambient room temperatures. If elevated temperaturesmust be encountered, Curie temperatures plotted on FIGURE 3 show thatwith lesser percentages of zinc ferrite Curie temperatures of 400 C. andabove may be obtained for high saturation flux density compositions. Thehigh saturation flux density area includes the areas of squareness, sothat-high saturation flux density may be obtained with or withoutsquareness as desired.

While exhaustive tests have not been made with cadmium ferrite as acomponent, research indicates that cadmium ferrite may be substituted ona one-for-one basis for zinc ferrite with substantially the sameresults.

There have thus been described improved ferrite materials exhibitingunexpected improvements in several of their useful magnetic properties.The proportions of the ingredients used should, in general, be withinthe percentage ranges given since use of other proportions results inproducts which either are not significantly improved or are inferior topreviously known ferrites.

Ranges of time and temperature of heating for the calcining andsintering steps have also been given. The size of the body influencesthe sintering time necessary to bring about the desired properties. Verysmall bodies require shorter sintering times than large bodies. Also,for both steps, the required time of heating is usually in inverse ratioto the temperature used. There is usually an optimum value for heatingtemperature and other parameters for each composition.

Having thus described improved ferromagnetic products and processes fortheir manufacture, what is claimed 1. A process for manufacturing shapedlithium nickel ferrites having hysteresis loops of substantiallyrectangular shape comprising maintaining said shaped ferrites in directcontact with a slab containing lithium during the firing thereof,wherein the percentage of lithium in said slab is at least equal to thepercentage of lithium in the lithium nickel ferrite.

2. A process for manufacturing shaped lithium nickel ferrites havinghysteresis loops of a squareness greater than 0.6 and relatively lowcoercivity comprising maintaining said shaped ferrites in direct contactwith a slab containing lithium during the firing thereof, wherein thepercentage of lithium in said slab is at least equal to the percentageof lithium in the lithium nickel ferrite.

3. The process of claim 1 wherein the lithium nickel ferrite materialconsists essentially of Li Fe O ZnFe O and NiFe O in the proportions ofabout 30 to about 98 mol percent Li Fe O about 2 to about 70 mol percentNiFe O and up to 40 mol percent ZnFe O 4. The process of claim 1 whereinthe lithium nickel ferrite material consists essentially of Li Fe O NiFeO and CdFe O in the proportions of about 65 to about 95 mol percent LiFe O about 7 to about 35 mol percent Nile 0,, and up to about 35 molpercent CdFe O 5. The process of claim 2 wherein the lithium nickelferrite material consists essentially of Li Fe O ZnFe O and NiFe O inthe proportions of about 30 to about 98 mol percent Li Fe Q, about 2 toabout 70 mol percent NiFe O and up to 40 mol percent ZnFe O 10 6. Theprocess of claim 2 wherein the lithium nickel ferrite material consistsessentially of Li Fe O NiFEzO and CdLFe O in the proportions of about toabout mol percent Li Fe O about 7 to about 35 mol percent NiFe O and upto about 35 mol percent CdFe O References Cited in the file of thispatent UNITED STATES PATENTS 2,549,089 Hegyi Apr. 17, 1951 2,565,861Leverenz et al Aug. 28, 1951 2,734,034 Crowley Feb. 7, 1956 2,736,708Crowley et al. Feb. 28, 1956 2,751,353 Gorter June 19, 1956 2,754,172Went et al. July 10, 1956 2,785,095 Pankove Mar. 12, 1957 2,882,234Gorter et al. Apr. 14, 1959 FOREIGN PATENTS 759,244 Great Britain Oct.17, 1956 1,110,819 France Oct. 19, 1955 1,115,324 France Dec. 26, 19551,116,092 France Ian. 23, 1956 1,116,093 France llan. 23, 1956 OTHERREFERENCES Ceramic Industry, vol. 58, No. 4, April 1952, pp. 130434.

Ceramic Industry, vol. 58, No. 5, May 1952, pp. 76-79.

Phillips Technical Review, vol. 16, No. 2, pp. 49-5 8.

1. A PROCESS FOR MANUFACTURING SHAPED LITHIUM NICKEL FERRITES HAVINGHYSTERESIS LOOPS OF SUBSTANTIALLY RECTANGULAR SHAPE COMPRISINGMAINTAINING SAID SHAPED FERRITES IN DIRECT CONTACT WITH A SLABCONTAINING LITHIUM DURING THE FIRING THEREOF, WHEREIN THE PERCENTAGE OFLITHIUM IN SAID SLAB IS AT LEAST EQUAL TO THE PERCENTAGE OF LITHIUM INTHE LITHIUM NICKEL FERRITE.